The present invention relates to an apparatus which records information in a recording media or reproduce the information from the recording media by holography and also to the recording media based on holography.
Studies concerning next generation storage techniques have been made, and attention has been focused on holographic recording techniques for digitally recording information by holography.
The hologram recording technique refers to a technique for recording information by an interference pattern which is generated when signal light having information on page data two-dimensionally modulated by a spatial light modulator is superimposed on reference light within a recording media and which causes refractive index modulation in the recording media.
In an information reproduction mode, when the recording media is exposed with the reference light used in a record mode with the same location, a hologram recorded in the recording media acts as a grating and produces diffracted light. The diffracted light is reproduced as the same light as signal light including phase information.
One of hologram recording techniques is disclosed, for example, in JP-A-2004/272268. This patent document recites a so-called angle multiplex recording system in which simultaneously when a signal light flux is focused on an optical-information recording media through a lens, reference light of collimated light flux is irradiated on the recording media to cause interference for hologram recording, and by changing an incident angle of the reference light to the optical recording media, different page data are displayed on a spatial light modulator for multiplexed recording. Also disclose in the cited document is a technique in which the signal light is focused through a lens to locate an opening (spatial filter) at the waist of the focused light, whereby intervals between adjacent holograms can be made short, thus increasing a recording density and a capacity when compared with those in the prior art angle multiplex recording system.
Another one of hologram recording technique is disclosed, for example, in WO2004/102542. This patent document represents an example of a shift multiplex system in which light from inner pixels is used as signal light and light from outer annular strip pixels is used as reference light in a single spatial light modulator, the both light fluxes are focused on an optical recording media through an identical lens, and the signal light and the reference light are interfered in the vicinity of the focal surface of the lens for hologram recording.